Biogas Production Enhancement from Mixed Animal Wastes at Mesophilic Anaerobic Digestion

Falah F. BaniHani et al. Int. Journal of Engineering Research and Applications www.ijera.com
ISSN: 2248-9622, Vol. 5, Issue 10, (Part - 3) October 2015, pp.167-173
www.ijera.com 167 | P a g e
Biogas Production Enhancement from Mixed Animal Wastes at
Mesophilic Anaerobic Digestion
Falah F. BaniHani*, Ahmad Qasaimeh**, Mohammad R. Abdallah/
Qasaimeh***
*(Department of Chemical Engineering, Al-Huson University College/Albalqa' Applied University, Jordan)
** (Department of Civil Engineering, Jadara University, Jordan)
***(Departments of Civil and Environmental Engineering, College of Engineering at Al Lith, Umm Al-Qura
University, Saudi Arabia)
ABSTRACT
In this work, the effect of mixing ratio of cattle dung (CD) and poultry droppings (PD) on biogas generation was
determined. Mixtures of various CD: PD ratios (100% : 0%; 50% : 50%; 60% : 40%; 80% : 20% and 0% :
100%) were prepared, analyzed and then aerobically digested for a period of 40 days. For each mixture,
fermentation was carried out in a 20 L capacity digester. Results showed that biogas was obtained from the
digestion of CD and PD alone, showing the biogas from CD was several times larger than that from PD.
Furthermore, the resulted biogas yields from mixtures were found a function of the CD : PD ratio, the yield from
the ratio 80 : 20 was the maximum. Biogas yields from the prepared mixtures were found and arranged from
larger to lower in the form of (CD : PD) ratios as follow: 80% : 20%; 100% : 0.0%; 60% : 40%; 0.0% :
100%;50% : 50%. Addition of CD to PD enhances the PD production of biogas, while addition of a small
portion of PD to CD gave the maximum yield, a result not determined in literature. In other hand, larger
additions of PD to CD reduced the biogas yield. The effect of pH was also determined and found better around
7.0. These results are in agreement with research work in literature.
Keywords- biogas generation; mixing ratio; anaerobic digestion; cattle dung; poultry droppings.
I. Introduction
Energy has always been a driving force for a
successful farming system. At present, government
policy is to minimize fossil fuel use and shift to clean
renewable energy. Research work in this line needs
attention. Biogas is a renewable energy derived from
organic matter, primarily cattle dung or any other
agro-residue. It is used in cooking, lighting, running
irrigation pump sets and in electricity generation. The
need for alternative renewable energy sources from
locally available resources cannot be over
emphasized. Appropriate and economically feasible
technologies that combine solid waste and
wastewater treatment and energy production can
simultaneously protect the surrounding water
resources and enhance energy availability[1,2,3].
Biogas technology in which biogas is derived through
anaerobic digestion of biomass, such as agricultural
wastes, municipal and industrial waste, is one of such
appropriate technology that can be adopted to ease
environmental problems and enhance energy
production. Biogas, which is a bio-energy produced
from a biomass, has several advantages over other
forms of renewable energies [4]. The anaerobic
fermentation of wastes for biogas production does not
reduce its value as a fertilizer supplement, since
available nitrogen and other substances remain in the
treated sludge [5,6], and most of the pathogens are
destroyed in the process of anaerobic digestion [7].
Several researches undertaken in anaerobic digestion
of wastes in developed countries have shown
technical feasibility of digestion of these wastes.
However, their studies in most often involve
regulation of temperature [8,9], pH adjustment [10],
pretreatment of waste [11] , and use of sophisticated
digesters. Of all the forms of solid organic waste, the
most abundant one is animal dung primarily from
small farms, and mainly ones that have pollution
problems originating from more tense waste disposal.
Research continues to focus on the treatment of cattle
dung for biogas production with possible
optimization methods, which can be used to enhance
the production for practical applications in
technology. Omar et al.[12] observed an
improvement in biogas yield up to 0.207 m3/ kg VS
added with average methane content of 65% in the
anaerobic treatment of cattle manure by addition of
palm oil mill effluent in a laboratory scale bioreactor.
In another study, Ounaar [13] obtained biogas
production of 26.9 m3 with an average methane
content of 61% during the anaerobic digestion of 440
kg of cow dung with an energy equivalent to 164.5
kWh. These results are encouraging for the use of
animal waste available to produce renewable energy
and clean environment. According to [14],
decomposition of 1 MT of grass waste can possibly
RESEARCH ARTICLE OPEN ACCESS

release 50 - 110 m3 of carbon dioxide and 90 -140
m3 of methane into the atmosphere. Methane is an
important greenhouse gas with the ability of global
warming around 25 times greater than that of carbon
dioxide, and its atmospheric concentration has been
increasing in to a range of 1 - 2% per year [15].
Conventional municipal solid waste (MSW)
management has been mainly disposal by land
filling[16]. However, waste from landfills has been
identified as the major source of anthropogenic
methane emission and an essential contributor to
global warming [15]. Therefore, the increased
production of MSW accompanied with
environmental and economic difficulties facing the
conventional methods of disposal have resulted in
great efforts to find alternative methods of disposal
[16]. The most promising alternative to incinerating
and composting of these solid wastes is to digest its
organic matter employing the anaerobic digestion
[17]. Anaerobic digestion for biogas production has
become a worldwide focus of research, because it
produces energy that is renewable and
environmentally friendly. Special emphasis was
initially focused on anaerobic digestion of MSW for
bioenargy production about a decade ago [18,19].
Anaerobic biological treatment can be an acceptable
solution because it reduces and stabilizes solid wastes
volume, produces biogas comprising mainly
methane, carbon dioxide and traces amount of other
gases [20]. In addition to biogas, a nutrient-rich
digestat is also produced which provide either
fertilizer or soil conditioner properties. Biological
treatment of MSW to biogas by anaerobic digestion
processes including source and mechanically sorted
MSW has been previously discussed [21]. Biogas
generation from biomass has been researched by
various scientists such as that focused on the quantity
and quality of biogas generated from several plant
and animal wastes. A number of researchers [2, 4, 22,
23] focus on the generation of biogas from a
particular waste type presupposing adequate
availability of such waste type for sustainable biogas
generation to satisfy the energy demand. More often,
most people in need of this type of technology do not
have enough particular type of waste to sustain and
satisfy their energy needs. Thus, for such people, a
need arises for a combination of whatever waste
types available at any particular time to produce a
biogas for their daily energy requirement. To fulfill
this need, some scientists have carried out various
researches on the effect of combining various types
of wastes on biogas generation. Some researchers
such as Kalia and Singh [19] could generate biogas
from a combination of cattle and horse dung, while
others studied biogas generation from piggery
manure and POME (palm oil mill effluent)
combination. In other hand, Iortyer [24]
experimented on partially substitution of cattle dung
with poultry droppings. They found the generation of
biogas to be satisfactory and in the following order:
biogas from cattle dung is larger than that from
mixture, and biogas from mixture is larger than that
from poultry droppings [25, 26]. Based on what
experimented by Iortyer [24] using only one mixing
ratio, therefore, the objectives of this research are to
optimize the production of biogas from a mixture of
cattle dung and poultry droppings at different mixing
ratios, and to determine the effect of mixing ratio of
poultry droppings and cattle dung on biogas
generation.
II. Materials and Methods
Poultry droppings PDs and cattle dungs CDs
used in this research work were randomly collected
from commercial farms in north Jordan. The PDs
were taken a farm few kilometers far from Irbid city
in north Jordan, while CDs were taken from A-dulel
cattle ranch in A-dulel town. The fresh substrates
were taken immediately to Laboratories in Al-Huson
University College for analysis. The main determined
parameters were moisture content (MC), total solid
(TS), volatile solid (VS), total Kjeldahl nitrogen
(TKN), carbon content (CC) and pH. Weights of 5kg
of mixed CD with PD were prepared in the following
ratios: 100% CD : 00% PD; 60% CD : 40% PD;
50% CD : 50% PD; 20% CD : 80% PD; and 00% CD
: 100% PD. These 5 kg prepared weights were then
mixed with equal weights of water giving total
samples, each having 10 kg with a ratio of 50:50
(w/w). These samples were then fed into five
identical cylindrical metallic anaerobic digesters
(reactors). Each digester has a height of 55 cm and a
diameter of 27.5 cm of an effective capacity of 25 L.
Each reactor had an appropriate port for feeding at
top and an effluent port for discharge at bottom
worked with the 10 kg samples for a period of 40
days to determine the effect of mixture ratio. The
body of the digester contains a stirrer for the mixing
of the substrate to enhance gas production. An exit
pipe is provided at the top of the smaller cylindrical
portion of the digester for biogas collection and
measurement. Other materials used for the
experiment include graduated transparent bucket and
measuring cylinder for measuring the volume of gas
production, hosepipe, thermometer, digital pH meter.
The 100% CD : 00% PD and 00 % CD : 100 % PD
are single substrate digestions used as data baseline
as recommended by [4,27]. The prevailing
temperature range was 24 to 34°C during the period
of study. The experiment was conducted at
uboptimum condition (ambient temperature without
any form of temperature regulation, pH adjustment,
pretreatment of substrates etc.). Volume
measurements of biogas produced were done by
water displacements. The method used was adopted
from [4, 26]. Biogas production was monitored and

measured for 40 days. Each experiment was repeated
twice and the average values obtained were taken in
the research work. Digital pH meters were used to
measure the pH of the digesting slurries every seven
days intervals. The ambient temperature was
measured using respectively a maximum and
minimum readings at 12.00 p.m and 12 a.m. The
initial MC was determined using the oven-dry
method at a temperature of 103 ± 2 oC for 24 h using
equation (1), while TS was computed using equation
(2) as shown below,
)2((%)100(%)
)1(
%100)(
(%)
MCTS
W
WW
MC
i
fi



where, i
W is initial weight and i
W is final weight.
Initial pH, carbon (%) and nitrogen were determined
before digestion. The percentage carbon was
determined using the Walkley-Black method and
percentage nitrogen by the micro-Kjiedhal method
[4,28]. The prevailing temperature range was 28ºC -
35ºC during the period of the study. More details on
the experimental setup can be found elsewhere [4].
The results of the analysis are shown in tables.1, 2
and 3.
III. Results and Discussion:
In this work, experimentation was started on
finding out the composition of the substrates.
Analysis for PD and CD were performed to find out
the MC, TS, VS, TKN, CC and pH values. Result of
this analysis is shown in (Table.1). For the important
pH effect on digestion process and biogas rate, the
pH values of the substrates were also determined at
seventh day during digestion and are shown in
(Table.2). In literature, many research work on
anaerobic digestion of waste showed that pH of
substrates has a strong influence on the production
rate and yield of biogas from substrate. The
methanogenic bacteria are known to be very sensitive
to pH. The pH of the substrates was measured on the
seventh day of digestion in accordance to [26], pH is
an indicator of system process stability of anaerobic
process. The values of the pH of the substrates
determined in this research (Table.2) fall within the
range of 6.5 to 7.2, which is the optimum pH for
anaerobic digestion. In the absence of some other
indicator, the pH value alone has been used to check
the digester environment and gas production is often
the highest when the pH is between 7.0 and 7.2 [26,
27]. Beyond these limits, digestion proceeds with less
efficiency. When the pH falls to 6 and below, the
efficiency drops rapidly during the acidic conditions,
which become inhibitory to methanogenic (methane
producing) bacteria. While at pH(= 7.0) there is a
balance in the population of the acidogenic (acid
producing) and methanogenic bacteria, which help to
convert the acids generated during anaerobic
Digestion into biogas . The digestion of these wastes
was carried out progressively without any noticeable
inhibition.
Table 1. The composition of the substrates
Cattle dungPoultry
dropping
Composition
6857Moisture Content MC ( %)
2138Total Solid TS (%)
14.812.2Volatile Solid VS (%)
3.19.5Total Kjeldahl Nitrogen TKN (mg/g)
11.45Carbon Content CC (%)
6.87.2pH
Table 2. Mean pH values of the cattle dung CD and poultry droppings PD mixtures on 7th day of digestion.
0% : 100%80% : 20%60% : 40%50% : 50%100% : 0%Digester CD : PD
7.26.57.06.66.8PH

Table 3. The C:N ratio of CD and PD.
Waste type Replicates
Mean321
12.2:110.6:114.6:111:1100:0 mixture of cattle and
poultry droppings
9.5:110.6:19.3:18.6:10:100 mixture of cattle and
poultry droppings
Table 4. Summary of biogas yield (in L/kg TS) from the mixtures of the cattle and poultry dropping
Analysis of nitrogen N in CD and PD were
performed and shown in (Table.3) in a form of
Carbon to Nitrogen ratios (C:N). The mean C:N
ratios for CD and PD were 11.4 and 9.5 respectively.
The C:N ratio for CD (11.4) was between 10:1 and
30:1, which is the favorable range for microbial
action [26] while that for PD (9.5) was slightly below
this range. This may have contributed to the lower
gas yield from the poultry droppings. The microbial
population involved in bioconversion process
requires sufficient nutrients in the form of nitrogen
and carbon to grow. If the nitrogen is not enough, the
bacteria will not be able to produce the enzymes
needed to utilize the carbon. While when there is too
much nitrogen, especially in the form of ammonia, it
can inhibit their growth [4, 24, 27]. The optimum
ratio of C:N given by Hawkes [29] is between 20:1
and 30:1. From the summary of the average values of
the measured day minimum and maximum
temperatures during the 40 detention days (Table 4),
the temperatures were ranged from 28 0C to 35 0C
with temperature fluctuations in the range of 3 0C to
5 0C. All these temperatures were within the
mesophyllic range and their fluctuations were within
a range not not to cause an adverse effect on biogas
production[4,30].
The total mean biogas yield for the mixture
ratios of the CD and PD are shown in (Table. 4). It
can be seen that the total mean biogas yield of
mixture ratio was in the following order: 80% CD :
20% PD > 100% CD : 0% PD > 60% CD : 40% PD >
50% CD : 50% PD > 0% CD : 100% PD. Generally,
as the proportion of poultry droppings increased in
the mixture, the biogas yield decreased. This is
because the mixture ratio of 0% CD : 100% PD
(poultry droppings only) gave a biogas yield lower
than that of the mixture ratio 100% CD : 0% PD
(cattle dung only). Therefore, the more it was
contained in the mixture the less total mean biogas
yield produced. This differs from the results obtained
by [4], who reported a higher yield of biogas from the
anaerobic digestion of cattle dung. However, the
mixture ratio of 80% CD : 20% PD which gave the
highest total biogas yield appeared to be the optimum
ratio at which cattle manure can be mixed with
poultry droppings to produce biogas that could
surpass even the amount produced by the cattle dung
alone.
As shown in (Fig.1), the first gas production
values were recorded on the 5th day for the cattle
dung only, while for the mixtures 50% CD : 50% PD,
60% CD : 40% PD, 80% CD : 20% PD and poultry
droppings only were recorded on the 3rd, 4th, 1st and
2nd days respectively. The highest daily mean biogas
yield value on any day of the 40-day detention
obtained from 80% CD : 20% PD mixture (0.198
L/Kg TS), while the next highest value (1.88 L/Kg
TS) was obtained from the cattle dung. The lowest
value (1.32 L/Kg TS) was given by the mixture 50%
CD : 50% PD.
Mean
(L/kg TS)
3 (L/kg
TS)
Replicates
2 (L/kg TS)
1 (L/kg
TS)
Min/Max.
Temp. TcWaste Type
2.2512.2312. 3182.34024-28100:0 mixture of CD : PD (cattle dung
only)
1.8371.9351.8531.72625-300:100 mixture of CD : PD ( poultry
droppings only)
1.6681.8831.5091.61224-2750:50 mixture of CD : PD
2.1582.2712.0302.17324-2960:40 mixture of CD : PD
2.8232.8492.8942.71225-2880:20 mixture of CD : PD

Figure 1. Effect of the mixture ratios of cattle dung CD and poultry droppings PD on mean daily biogas
yield
During the first 5 days of (CD : PD) digestion
(Fig.2), gas production of the different mixing ratios
are seen and the 0% CD : 100% PD (poultry
droppings alone) digestion showed the highest biogas
yield. This agrees well with [31], who reported that
poultry dropping waste degrades faster than cattle
dung waste. However on 10th day, the 100% CD :
00% PD digester (cattle dung alone) took the lead by
producing a total biogas yield in comparison to 0%
CD P : 100% PD digester. This lead is seen continued
during the 40 days period. This confirms in this work
the ability of the cattle dung CD to produce more
biogas than poultry dropping PD with time. Among
all Digesters, the one having the 80% CD : 20% PD
showed the highest total volume of biogas
production. This is slightly higher than the biogas
produced by the digester having the 100% CD : 00%
PD. In other hand, the digester having the 60% CD :
40% PD produced lower total volume of biogas but is
still higher than the biogas produced from the
digesters having the 0% CD : 100% PD and 50% CD
: 50% PD respectively.
Figure 2. Cumulative biogas yield of cattle dung with poultry dropping with their mixing ratio
From the beginning and to the end of the 40 days
during the experiment (Fig.1), the digester having the
100% CD : 00% PD after maintaining maximum
experienced a great decline in gas production in the
end part of the experiment. This shows the tendency
of the 80% CD : 20% PD digester to produce more
gas than the single substrate digestion of cow dung
CD with time; here addition of 20% PD enhanced the
CD production of biogas. While more addition of PD
with CD reduces the biogas production, an example
is the 50% CD : 50% PD digester, showing the least
gas yield but still better than the 0% CD : 100% PD
yield. For all used ratios of (CD : PD) in digesters
(Fig.1), production of biogas is shown maximum in
0
0.5
1
1.5
2
2.5
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 40
Time / Days
Biogasproduction(L)
100%CD+0%PD
80%CD+20%PD
60%CD+40%PD
50%CD+50%PD
0%CD+100%PD
0
2
4
6
8
10
12
14
16
18
0 3 6 9 12 15 18 21 24 27 30 33 36 39
Time/Days
cumulativegasproduction,(L)
80%; 20%
100% :0%
60%: 40%
0%:100%
50%:50%

the period between 15 to 27 days with time. The
order of gas production for the CD : PD ratios is
resulted as follow: 80% CD : 20% PD > 100% CD :
0% PD > 60% CD : 40% PD > 00% CD : 100% PD >
50% CD : 50% PD.
IV. Conclusion
Mixing of cattle dung and poultry droppings
have generally increased the biogas yield compared
with the biogas yields from pure cattle dung and
poultry droppings. The potentials of the maximum
biogas production from the cattle dung and poultry
dropping mixtures are found in the following order:
80% CD : 20% PD > 100% CD : 00% PD > 60% CD
: 40% PD > 50% CD : 50% PYD > 00% CD : 100%
PD. The maximum biogas yield is attained with
mixtures with a ratio of 80% CD : 20% PD, while the
second is pure CD (100% CD : 00% PD). Such result
indicates that addition of small portions of PD to CD
enhances the CD production of biogas. In other hand
increases in CD addition to PD enhances the PD
production of biogas until reaching the 80% CD :
20% PD ratio. Pure PD gives the minimum biogas
production, while pure CD needs a small portion
addition of PD. This in a long way not only solves
the problem of adequate energy lack for poor rural,
but also helps in maintaining the safe and clean
disposal of such waste. However, longer digestion
detention periods may be required at other
conditions, because gas production has not ceased for
the digesters, especially for the 20% CD : 80% PD
digester. This can be left to further research work.
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